Siting classification for Surface Ob Observing Stations on Land i St ti L d Michel Leroy, Météo-France
Content of the presentation Q Quality factors of a measurement lit f t f t Site representativeness Siting classification Experience of Météo-France with this classification Experience of Météo France with this classification Quality factors : instrumental performance, maintenance and calibration – Maintained performance classification M i t i d f l ifi ti « Simple » metadata to document a network Exemples from Météo-France Exemples from Météo France Conclusion JMA/WMO RAII QM-OBS
Quality factors of a measurement The intrinsic characteristics of sensors or Th i i i h i i f measurement methods The maintenance and calibration needed to maintain the system in nominal to maintain the system in nominal conditions. The site surroundings – Improper siting can jeopardize the quality of Improper siting can jeopardize the quality of the data. JMA/WMO RAII QM-OBS
Site representativeness Exposure rules from CIMO recommendations Exposure rules from CIMO recommendations. But not always followed and not always possible to follow, depending on the geographical situation. Site classification metadata “easy” to archive and to use Site classification, metadata easy to archive and to use. – A class 1 site can be considered as a reference site – A class 5 site is a site where nearby obstacles create an inappropriate environment for a meteorological measurement that is intended to be g representative of a wide area. – Class 2, 3 and 4 are intermediate – The smaller is the siting class, the higher is the representativeness of the measurement for a wide area measurement for a wide area. Site classification was first designed by Météo-France in 1998. It is now applied or under consideration by several countries (France, USA, Canada, Switzerland Norway Switzerland, Norway, …). It was discussed and updated within an ad hoc ) It was discussed and updated within an ad-hoc Working Group on WIGOS Pilot Project in October 2009. It is proposed for consideration by CIMO-XV. JMA/WMO RAII QM-OBS
Each parameter being measured at a site has its own class. The rating of each class should be reviewed periodically: – A systematic yearly visual check is recommended. If some aspects of the environment have changed, a new classification process is necessary A complete update of the site classes should be done at least every 5 years. The classification is occasionally completed with an estimated uncertainty due to siting: additional estimated uncertainty added by y g y y siting up to xx Complex terrain or urban area generally leads to high class number Complex terrain or urban area generally leads to high class number. In such cases, an additional flag “S” can be added to class numbers 4 or 5 to indicate Specific environment or application (i.e. 4S) JMA/WMO RAII QM-OBS
What to do with “natural” obstacles? Th The primary objective is to document the presence of obstacles i bj ti i t d t th f b t l close to the measurement site Therefore, natural relief of the landscape may not be taken into y account, if far away (i.e. > 1 km) Does a move of a station by the 500 m change the class obtained? – If no, the relief is a natural characteristic of the area and is not taken If no the relief is a natural characteristic of the area and is not taken into account – Applies for the same obstacles, not new ones. JMA/WMO RAII QM-OBS
Classification for air temperature and humidity Obstacles around the screen influence the irradiative balance of the Ob t l d th i fl th i di ti b l f th screen. Neighbouring artificial interfaces may heat the air and should be g g y avoided. It was decided to not take into account the statistical wind situation at the site. at the site – Low wind speed may occur at the time of occurrence of extreme temperatures. – The classification should remain as simple as possible to use Th l ifi ti h ld i i l ibl t JMA/WMO RAII QM-OBS
Air temperature and humidity, class 1 Fl t h Flat, horizontal land, surrounded by an open space i t l l d d d b Ground covered with natural and low vegetation, representative of the region g Away from artificial heat sources Away from projected shade when the sun is higher than 5° JMA/WMO RAII QM-OBS
Air temperature and humidity, class 2 and 3 Class 2 Class 3 (additional estimated uncertainty added by siting up to 1°C) JMA/WMO RAII QM-OBS
Air temperature and humidity, class 4 and 5 Class 4 (additional estimated uncertainty added by siting up to 2°C) Class 5 (additional estimated uncertainty added by siting up to 5°C) – When not class 4 JMA/WMO RAII QM-OBS
Classification for precipitation Wind is the greatest source of disturbance in precipitation measurements, due to the effect of the instrument on the air flow Class 1, preferred Or JMA/WMO RAII QM-OBS
Precipitation, class 2 and 3 Class 2 (additional estimated uncertainty added by siting up to 5%) Class 3 (additional estimated uncertainty added by siting up to 15%) JMA/WMO RAII QM-OBS
Precipitation, class 4 and 5 Class 4 (additional estimated uncertainty added by siting up to 25%) Class 5 (additional estimated uncertainty added by siting up to 100%!) JMA/WMO RAII QM-OBS
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Classification for wind measurements R Roughness classification : Davenport, see CIMO Guide, WMO Doc h l ifi ti D t CIMO G id WMO D n ° 8 Environment classification The presence of obstacles (almost invariably) means a reduction in average wind readings, but less significantly affects wind gusts. The classification assumes measurement at 10 m The classification assumes measurement at 10 m. When measurement are carried out at lower height (such as at 2 m for agro-climatological purposes), a class 4 or 5 is to be used, with flag S (Specific situation) When numerous obstacles higher than 2 m are present, it is recommended that sensors should be placed 10 m above the recommended that sensors should be placed 10 m above the average height of the obstacles. JMA/WMO RAII QM-OBS
Wind, class 1 and 2 Class 1 Class 2 (additional estimated uncertainty added by siting up to 30%, possibility to apply correction) ibilit t l ti ) JMA/WMO RAII QM-OBS
Wind, class 3 and 4 Class 3 (additional estimated uncertainty added by siting up to 50%, correction cannot be applied) pp ) Class 4 (additional estimated uncertainty added by siting greater than 50%) JMA/WMO RAII QM-OBS
Wind, class 5 Cl Class 5 (additional estimated uncertainty cannot be defined) 5 ( dditi l ti t d t i t t b d fi d) Site not meeting the requirements of class 4 Site not meeting the requirements of class 4 JMA/WMO RAII QM-OBS
St-Sulpice North East JMA/WMO RAII QM-OBS
West West St-Sulpice South South JMA/WMO RAII QM-OBS
St-Sulpice. Documentation of obstacles Class 4 for wind Class 4 for wind. New Radome AWS settled at a distance of 60 m, away from the woods class 3 JMA/WMO RAII QM-OBS
Saint Sulpice , DIRCE Ratio of mean wind speed (10 min ) between Patac et Xaria Ratio of mean wind speed (10 min.) between Patac et Xaria South winds North winds JMA/WMO RAII QM-OBS
Classification for global and diffuse solar radiation radiation Cl Close obstacles have to be avoided b t l h t b id d Shading due to the natural relief is not taken into account An obstacle is considered as reflecting if its albedo is greater than An obstacle is considered as reflecting if its albedo is greater than 0.5 Class 1 JMA/WMO RAII QM-OBS
Global and diffuse radiation Class 2 Class 3 JMA/WMO RAII QM-OBS
Global and diffuse radiation Cl Class 4 4 Class 5 – Shade projected during more than 30% of the daytime, for at least one p j g y , day of the year JMA/WMO RAII QM-OBS
Classification for direct radiation and sunshine duration sunshine duration Class 1 Class 2 JMA/WMO RAII QM-OBS
Direct radiation and sunshine duration Class 3 Class 4 JMA/WMO RAII QM-OBS
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